Evaluation of the Finnish versions of the functional indices BASFI and DFI in spondylarthropathy.

The aim of the study was to compare and evaluate the usefulness of Finnish versions of two functional indices used in spondylarthropathies. Seventy consecutive inpatients with different kinds of spondylarthropathies filled in self-administered questionnaires: the Bath Ankylosing Spondylitis Functional Index (BASFI) and the Dougados Functional Index for spondylarthropathies (DFI). Cronbach's alpha as a coefficient of internal consistency was analysed for BASFI and DFI. Test-retest reliability was evaluated in 30 patients. For validity the functional indices were compared with the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), erythrocyte sedimentation rate (ESR), spinal movement measures of chest expansion (CE), Schober S1 test and occiput-to-wall distance (OWD), and radiological changes in the lumbar spine (RTGLS) and sacroiliac joints (RTGSI). The reproducibility of the indices BASFI and DFI was good; the intraclass correlation coefficient (ICC) for reliability was 0.99 and 0.98, and the coefficient of internal consistency (Cronbach's alpha) was 0.94 for both BASFI and DFI. The functional indices correlated well with each other, r = 0.85 (95% CI 0.78-0.90). Validity in terms of correlation coefficients between disease activity index BASDAI and functional indices BASFI and DFI was 0.74 (95% CI 0.60-0.84) and 0.69 (95% CI 0.53-0.80), respectively. BASFI and DFI correlated with spinal mobility measurements and RTGLS, but DFI did not correlate with RTGSI. Neither BASFI nor DFI correlated with ESR and disease duration, and only DFI correlated with age. In conclusion, BASFI and DFI are reliable and valid for Finnish inpatients with spondylarthropathies. It is important to know that cultural differences do not reduce the usefulness of these indices.